This sailboat calculator is great fun to noodle with!

http://www.image-ination.com/sailcalc.html

I think the results should be taken with a large grain of salt, however.  The calculation makes no effort to locate the center of gravity or determine freeboard.  If this were a physics problem from my college days, I think I'd get a tongue lashing for trying to make this approach float!  According to the calculator, a P-15 with a 400# payload is more stable than an M-15 with the same...I think not!  I guess there's no substitute for turning boats over and seeing what happens.  My friend Scott pointed out that floatation run up the mast can make a great difference in these situations-good point made.  So, any intrepid volunteers willing to turn their pride and joy over in the interests of science?  I would, naturally, except the lake's mighty cold now and the water level is down...

Tongue firmly in cheek

Steve Tyree, P-15 #2098 "Amy Ann"